Method and apparatus for performing vertical handover in sdr terminal

ABSTRACT

Disclosed are a method and apparatus for allowing a Software Defined Radio (SDR) terminal to perform a vertical handover between different services. The vertical handover method includes: receiving a handover request from an application service which is currently being executed; selecting a new application service which is a handover target from among a plurality of application services, in response to the handover request; installing the new application service in the SDR terminal so that the new application service is executable by the SDR terminal; and performing a handover to the new application service. Accordingly, since handover is performed seamlessly between different services, continuity of service may be ensured.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. §119(a) of KoreanPatent Application No. 10-2008-120577, filed on Dec. 1, 2008, thedisclosure of which is incorporated by reference in its entirety for allpurposes.

BACKGROUND

1. Field

The following description relates to a Software Defined Radio (SDR)terminal, and more particularly, to a method and apparatus for allowinga Software Defined Radio (SDR) terminal to perform a vertical handoverbetween different services.

2. Description of the Related Art

The structure of a Software Defined Radio (SDR) terminal is based on aSoftware Communication Architecture (SCA) core framework.

SCA is a standardized communication software proposed by the U.S. JointTactical System (JTRS) Joint Program Office (JPO) for the purpose ofimproving inter-operability between communication systems and reducingcosts for development and design. A SDR system seeks high compatibilityand inter-operability between configuration modules by adopting SCA as asoftware framework standard.

Vertical handover (VHO) means handover between different services. Asmobile communication services diversify, there are cases where users whohave subscribed with two or more mobile communication services. And,users want to get mobile communication services seamlessly whilemigrating between different mobile communication services as necessary.

For example, if a user who uses an IEEE 802.11 Wireless LAN (WLAN)indoors changes to the service of an IEEE 802.16e Mobile WiMAX servicewhen he or she goes outdoors, then this means that a handover betweenthe two services has occurred.

A recently proposed vertical handover, which is based on the IEEE 802.21standard, locates Media Independent Handover (MIH) between a MediumAccess Control (MAC) layer and a Layer 3 (L3) layer. Also, the methodcauses MIH to standardize and accept handover-associated primitives ofvarious MAC layers for each media so that the L3 layer can controlhandover between services through a single method. The 802.21-basedvertical handover enables seamless handover between a plurality ofMAC/PHY protocols installed in advance under the control of a singleMIH.

A SDR terminal is an open system designed to flexibly receive variouscommunication services with a single piece of hardware. A SDR terminalhas been initially provided in the is form of Bare Machine. A SDRterminal downloads protocols for a desired service as necessary, andthen installs therein and executes them. The SDR terminal is expected tobe a system which is flexibly adaptable to the current mobilecommunication environment including frequent creations and abandoning ofvarious mobile communication services.

The 802.21-based vertical handover technique is structured under thebasic assumption that protocol sets of relevant mobile communicationservices should be installed in a terminal. For example, when a verticalhandover occurs between 802.11 and 802.16e, 802.11 MAC/PHY and 802.16ehave to be installed in a corresponding terminal and be in a standbystate for execution to respond to MIH commands. Accordingly, if thenumber of service objects that allow vertical handover is N, then Nnumber of MAC/PHY protocols have to be installed in advance in thecorresponding terminal.

However, in the 802.21-based vertical handover technique, since allprotocols of all services with which a user subscribes have to be loadedinto hardware, it may cause unnecessary waste of hardware resources,resulting in inefficient resource management. Also, since whenever achange occurs in use of service, such as service subscription or servicesecession, the corresponding set of protocols has to be newly installedor deleted, and as such an inconvenience with regards to requiredupdates or replacements is created.

Meanwhile, in the case of the SDR terminal, there are advantages inthat, when a service changes to another one, not too many protocols arerequired to be loaded and replacement of hardware is also not required.In order to perform a seamless vertical handover, a service that is tobe handed over has to be recognized in advance. Otherwise, an additionaltime for installing an application service for a service that is to behanded over would be required. This is because a SDR terminal requires atime to download and install protocol sets of a required service.Consequently, since any time consumed to install new applicationservices delay handover, continuity of service may not be ensured.

SUMMARY

The following description relates to a method and apparatus for allowinga Software Defined Radio (SDR) terminal to perform seamless verticalhandover.

According to an exemplary aspect, there is provided a vertical handovermethod which is performed by a Software Defined Radio (SDR) terminalcapable of selectively executing at least one of a plurality ofapplication services, the method including: receiving a handover requestfrom an application service which is being currently executed; selectinga new application service which is a handover target from among theplurality of application services, in response to the handover request;installing the new application service in the SDR terminal so that thenew application service is executable by the SDR terminal; andperforming a handover to the new application service.

The selecting of the new application service includes preferentiallyselecting an application service which has not recently been installedin the SDR terminal, based on installation history information aboutapplication services executable in the SDR terminal.

The performing of the handover includes performing the handover when aninstallation completion message is received from the new applicationservice.

The vertical handover method, before the performing of the handover,further includes performing channel-scanning on the new applicationservice, wherein the performing of the handover comprises performing thehandover when it is determined according to the result of thechannel-scanning that the handover is allowed.

The vertical handover method, after the performing of thechannel-scanning, further includes if the channel-scanning fails,transmitting a service stop command to the new application service.

According to another exemplary aspect, there is provided an apparatusfor vertical handover which is included in a Software Defined Radio(SDR) terminal capable of selectively executing at least one of aplurality of application services, including: at least one serviceexecution unit which is software-reconfigurable and capable of executingvarious application services; and a handover execution unit to perform ahandover between the application services that are executable by the SDRterminal; and a Software Communication Architecture (SCA) coreframework, when receiving a handover request from the service executionunit which executes an application service, to generate a serviceexecution unit for executing an application service that is a handovertarget, and to control execution of a handover of the SDR terminal inconnection with the service execution unit and the handover executionunit.

Accordingly, due to the feature of a SDR terminal which is that it canprovide various application services without having to load manyprotocols, there is provided flexibility in joining or leaving services.

Furthermore, by enabling a SDR terminal to perform seamless handoverbetween different services, service continuity is ensured.

Other objects, features and advantages will be apparent from thefollowing description, the drawings, and the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an apparatus for verticalhandover according to an exemplary embodiment.

FIG. 2 is a flowchart illustrating a handover method according to anexemplary embodiment.

FIG. 3 is a flowchart illustrating a handover method afterchannel-scanning fails, is according to an exemplary embodiment.

FIG. 4 is a flowchart illustrating a procedure of stopping a previousservice after a handover is completed in the handover method.

Elements, features, and structures are denoted by the same referencenumerals throughout the drawings and the detailed description, and thesize and proportions of some elements may be exaggerated in the drawingsfor clarity and convenience.

DETAILED DESCRIPTION

The detailed description is provided to assist the reader in gaining acomprehensive understanding of the methods, apparatuses and/or systemsdescribed herein. Various changes, modifications, and equivalents of thesystems, apparatuses, and/or methods described herein will likelysuggest themselves to those of ordinary skill in the art. Also,descriptions of well-known functions and constructions are omitted toincrease clarity and conciseness.

FIG. 1 is a block diagram illustrating an apparatus for verticalhandover according to an exemplary embodiment. Referring to FIG. 1, thevertical handover apparatus includes a Software CommunicationArchitecture (SCA) core framework 10, a handover performing unit 20 anda service execution unit 30.

The SCA core framework 10 may be middleware that works at the hub of aSoftware Defined Radio (SDR) terminal. In the current embodiment, theSCA core framework 10 performs domain management, device management,file management, management of application programs, etc. That is, theSCA core framework 10 plays a key part in operating the SDR terminal tofulfill the concept of SDR. Also, the SCA core framework 10 controls thehandover performing unit 20 and the service execution unit 30.

The handover performing unit 20 includes a handover assembly controller22, a layer-3 (L3) resource 26 and a Media Independent (MIH) resource24. The handover performing unit 20 is composed of service-independentlayers. The L3 resource 26 may control all operations associated withhandover of the SDR terminal. The MIH resource 24 performs handoverprimitive processing between 802.21 services. The handover assemblycontroller 22 processes SCA control commands between the L3 resource 26,MIH resource 24 and SCA core framework 10. Also, the handover assemblycontroller 22 relays communications between lower resources of theservice execution unit 30 which will be described later.

In the current embodiment, the handover performing unit 20 is downloadedand installed in the SDR terminal when the SDR terminal is initialized.The downloading and installing of the handover performing unit 20 aredone unconditionally regardless of the types of services that are to beinstalled or started by the service execution unit 30.

The service execution unit 30 includes a service assembly controller 32,a Medium Access Control (MAC) resource 34 and a Physical Layer (PHY)resource 36. The MAC resource 34 and PHY resource 36, which areprotocols dependent on communication services, are respectively incharge of MAC and PHY. The service assembly controller 32 processes SCAcontrol commands between the MAC resource 34, PHY resource 36 and SCAcore framework 10. Also, the service assembly controller 32 relayscommunications with the resources of the handover performing unit 20.

The service execution unit 30 is installed as one of communicationservices with which a terminal's user has subscribed. Generally, while aservice is being used, a corresponding service execution unit 30 isselected, installed and started, but while a handover is beingprocessed, the service currently being used and another service which isa handover target may be simultaneously started or installed.

In the current embodiment, ‘application services’ are not limited tospecific application services which fall under the concept of SDR. Thatis, in the current embodiment, the ‘application services’ may beselected, downloaded and installed arbitrarily by users. According to anembodiment, if a user selects an 802.11 Wireless LAN service as thefirst service execution unit 30 a, the first service execution unit 30 aexecutes the 802.11 WLAN service and accordingly the first assemblycontroller 32 a, and the first MAC resource 34 a and the first PHYresource 36 a are installed to be suitable for the 802.11 WLAN service.

In the current embodiment, a communication channel is establishedbetween the handover assembly controller 22 and the service assemblycontroller 32 a and 32 b. The communication channel is forcommunications between the MAC resource 34 of the service execution unit30 which is to perform application services and the L3 resource 26 andthe MIH resource 24 which form the handover execution unit 20.Primitives associated with 802.21 vertical handover are transmitted andreceived between the MAC resource 34 and MIH resource 24, and signalinformation or traffic data, etc. are transmitted and received betweenthe MAC resource 34 and L3 resource 26. As described above, messagetransmission/reception between the L3 resource 26, the MIH resource 24,the MAC resource 34 and the PHY resource 36 may be performed under thecontrol of the handover assembly controller 22, the first serviceassembly controller 32 a and the second service assembly controller 32b.

Hereinafter, a method of supporting handover will be described withreference to FIGS. 2, 3 and 4.

FIG. 2 is a flowchart illustrating a handover method according to anexemplary embodiment. First, it is assumed that a terminal is performinga first application service. While the terminal is performing the firstapplication service, a MAC resource 34 a of a first service executionunit 30 a may detect if a service radio signal is weak (operation 300).If the MAC resource 34 a determines that a service radio signal is weak,the MAC resource 34 a transmits a message indicating that the serviceradio signal is weak to a first service assembly controller 32 a, thustransmitting a handover request (operation 302). At this time, the MACis resource 34 a may transmit as a handover request message 802.21primitive Link_Going_Down.indication to the first service assemblycontroller 32 a. Then, the first service assembly controller 32 atransmits the received handover request as a Link_Going_Down.indicationmessage having the same primitive format to the handover assemblycontroller 22 of the handover performing unit 20 (operation 305).

Then, the handover assembly controller 22 requests installation of a newservice to a SCA core framework 10 (operation 310). At this time, thehandover assembly controller 22 may request installation of a newservice to the SCA core framework 10 by transmitting aSC_New_Service_Installation_Request message to the SCA core framework10.

Then, the SCA core framework 10 selects and installs one of serviceswith which the terminal has subscribed, based on a Software ComponentDescription (SCA) and a Software Assembly Descriptor (SAD) of a domainprofile, in response to the service installation request (operation320). The SCA core framework 10 may preferentially select an applicationservice which has been not recently been installed in the terminal,based on installation history information about application servicesthat have been previously installed in the terminal. That is, the SCAcore framework 10 may exclude services which are currently being servedor which have recently failed in a channel-scan.

Then, the SCA core framework 10 installs an assembly controller 32 a, aMAC resource 34 a and a PHY resource 36 a to execute the applicationservice for the new service, and if the installation is completed,transmits a SC_Start message to the second service assembly controller32 b to instruct execution of the application service (operation 330).Then, the second service assembly controller 32 b transmits a SC_Startmessage which is an operation start command to the MAC resource 34 b andthe PHY resource 36 b, thus starting the operation of the MAC resource34 b and the PHY resource 36 b (operations 340 and 345).

When the installation and execution of the new service, that is, thesecond service is execution unit 30 b are completed, the SCA coreframework 10 transmits a SC_New_Service Installation Response message tothe handover assembly controller 22 of the handover performing unit 20,thereby informing the handover assembly controller 22 that installationof the new service has been completed (operation 350).

Then, the handover assembly controller 22 relays aLink-Going_Down.indication message to the MIH resource 24 (operation360) and again transfers the Link-Going_Down.indication message to theL3 resource 26 (operation 365). In this way, before a report messageindicating radio signal weakness of the MAC layer of the first serviceexecution unit 30 a which has been previously activated is transmittedto the MIH and L3 layers, the SCA core framework 10 can startinstallation of another service which is a handover target.

Thereafter, the MIH resource 24 and L3 resource 26 of the handoverperforming unit 20 perform a channel-scanning procedure on the servicethat is to be executed in an 802.21 channel, that is, in the secondservice execution unit 30 b (operation 370). The channel-scanningprocedure is based on the 802.21 standard. When performing thechannel-scanning procedure, communications between the MIH resource 24and L3 resource 26 which are the lower resources of the handoverassembly controller 22, and the MAC resource 34 a and the PHY resource36 a which are the lower resources of the assembly controller 32 a areperformed through the relay of the handover assembly controller 22 andassembly controller 32 a.

After the channel-scanning, the L3 resource 26 of the handoverperforming unit 20 checks if the channel-scanning is successful. If thechannel-scanning is successful, it is determined that the correspondingservice is a radio channel allowing a handover (operation 380) andaccordingly, 802.21 ranging, registration and handover procedures aresequentially performed, so that a handover on the service is completed(operation 390).

FIG. 3 is a flowchart illustrating a handover method afterchannel-scanning fails, is according to an exemplary embodiment.

After the channel-scanning, if the L3 resource 26 of the handoverperforming unit 20 determines that the channel-scanning fails (operation400), this means that a handover to the corresponding radio channel isdisallowed and accordingly a new service has to be selected. Thus, aSC_Other_Link_Request message indicating that a new service has to beselected is generated and transmitted to the handover assemblycontroller 22 (operation 410).

Then, the handover assembly controller 22 transmits aSC_New_Service_Installation_Request message for requesting installationof another new service to the SCA core framework 10 (operation 415).

Then, the SCA core framework 10 transmits a SC_Stop message for stoppingservice execution, to the assembly controller 32 b of the second serviceexecution unit 30 b which has failed in channel-scanning (operation420). The assembly controller 32 b of the second service execution unit30 b transmits the SC_Stop message for stopping service execution to theMAC resource 34 b and the PHY resource 36 b which are the lowerresources of the assembly controller 32 b (operations 422 and 424).Accordingly, the execution of the second service is stopped, and the SCAcore framework 10 tears down the corresponding service (operation 430).

Then, the SCA core framework 10 selects one of services with which theSDA terminal has subscribed, based on a SCD and a SAD of domain profilesof the SCA core framework 10, and installs the selected service(operation 440). At this time, the SCA core framework 10 preferentiallyselects an application service which has not been recently installed inthe terminal, based on installation history information aboutapplication services that have been previously installed in theterminal, in order to prevent the first service that is being currentlybeing served or the second service that has recently failed inchannel-scanning from being selected. This is to prevent any unnecessaryprocesses from occurring.

In the current embodiment, the SCA core framework 10 selects a thirdservice and is generates a third service execution unit 30 c associatedwith the third service. In detail, an assembly controller 32 c, a MACresource 34 c and a PHY resource 36 c for executing the third serviceare generated and installed. If installation of the third serviceexecution unit 30 c is completed (operation 440), the SCA core framework10 transmits a SC_Start message to the assembly controller 32 c of thethird service execution unit 30 c and causes the assembly controller 32c to operate (operation 450). Also, the assembly controller 32 ctransfers the SC_Start message to the MAC resource 34 c and the PHYresource 36 c to operate them (operations 460 and 465).

If the installation and execution of the new service, that is, the thirdservice are completed, the SCA core framework 10 transmits aSC_New_Service_Installation_Response message to the handover assemblycontroller 22 of the handover execution unit 20, thus informing thehandover assembly controller 22 that installation of the new service hasbeen completed (operation 470). Then, the handover assembly controller22 transmits a SC_Other_Link_Response message to the L3 resource 26,thus informing the L3 resource 26 that installation of the new servicehas been completed (operation 475).

In summary, when the channel scanning of the previouslyinstalled/started second service fails, the second service is torn downand stopped, and another service, that is, the third service isselected, installed and started.

Thereafter, channel-scanning is performed on the third service(operation 480), it is determined whether the channel scanning issuccessful (operation 490), and a handover is performed according to theresult of the determination (operation 495).

If the channel-scanning again fails, the process returns to operation5400 of selecting a new service and the procedure described above isrepeated. The procedure is repeated until a service is found on whichchannel scanning is successful or until a service with which a usersubscribes does no longer exist in the SCD and SAD of the SCA coreframework 10.

FIG. 4 is a flowchart illustrating a procedure of stopping a previousservice after a handover is completed in the handover method.

If a handover to a second or third service has been completed, radiosignals associated with the first service are disconnected. Accordingly,the MAC resource 34 a of the first service execution unit 30 a maydetect the disconnection of radio signals, and transfers any result ofdetection to the handover assembly controller 22 of the handoverexecution unit 20 via the assembly controller 32 a (operation 500). Atthis time, the result of the detection may be transmitted in the form ofa Link_Down.indication message to the handover assembly controller 22.

Then, the handover assembly controller 22 transmits aSC_Service_Teardown_Request message as a request for tearing down thefirst service to the SCA core framework 10 (operation 510). Then, theSCA core framework 10 transmits a SC_Stop message to the assemblycontroller 32 a of the first service execution unit 30 a, thusrequesting the assembly controller 32 a to stop execution of the firstservice (operation 520). The assembly controller 32 a transfers theSC_Stop message to the MAC resource 34 a and the PHY resource 36 a, thusstopping the operation of the MAC resource 34 a and the PHY resource 36a (operation 522 and 524).

When the execution of the MAC and the PHY resources 34 a and 36 a of thefirst service execution unit 30 a is stopped, the SCA core framework 10performs a teardown procedure on the first service (operation 530).Then, the SCA core framework 10 transmits a SC_Service_Teardown_Responsemessage to the handover assembly controller 22 to inform that theteardown of the first service has been completed (operation 550). Then,the handover assembly controller 22 relays the Link_Down.indicationmessage received from the assembly controller 32 a of the first serviceexecution unit 30 a to the MIH resource 24 (operation 560).

Accordingly, before a signal disconnection report from the MAC resource34 a of the first service execution unit 30 a is transferred to the MIHresource 24 of the handover performing unit 20, the first serviceexecution unit 20 is torn down.

Meanwhile, the method for performing vertical handover in SDR terminaldescribed above can be implemented as a computer program. The computerprogram can be stored in computer-readable recording media and read andexecuted by a computer. The computer-readable recording media may beimplemented on a magnetic tape, an optical data storage, or the like.

It will be apparent to those of ordinary skill in the art that variousmodifications can be made to the exemplary embodiments of the inventiondescribed above. However, as long as modifications fall within the scopeof the appended claims and their equivalents, they should not bemisconstrued as a departure from the scope of the invention itself.

1. A vertical handover method which is performed by a Software DefinedRadio (SDR) terminal capable of selectively executing at least one of aplurality of application services, the method comprising: receiving ahandover request from an application service which is being currentlyexecuted; selecting a new application service which is a handover targetfrom among the plurality of application services, in response to thehandover request; installing the new application service in the SDRterminal so that the new application service is executable by the SDRterminal; and performing a handover to the new application service. 2.The vertical handover method of claim 1, wherein the selecting of thenew application service comprises preferentially selecting anapplication service which has not recently been installed in the SDRterminal, based on installation history information about applicationservices executable in the SDR terminal.
 3. The vertical handover methodof claim 2, wherein the selecting of the new application servicecomprises selecting the new application service based on a SoftwareComponent Descriptor (SCD) and a Software Assembly Descriptor (SAD) of adomain profile of the SDR terminal.
 4. The vertical handover method ofclaim 1, wherein the performing of the handover comprises performing thehandover when an installation completion message is received from thenew application service.
 5. The vertical handover method of claim 1,before the performing of the handover, further comprising performingchannel-scanning on the new application service, wherein the performingof the handover comprises performing the handover when it is determinedaccording to the result of the channel-scanning that the handover isallowed.
 6. The vertical handover method of claim 5, after theperforming of the channel-scanning, further comprising: if thechannel-scanning fails, transmitting a service stop command to the newapplication service; and stopping installation of the new applicationservice according to the service stop command.
 7. The vertical handovermethod of claim 6, further comprising if the channel-scanning fails,selecting another new application service other than the new applicationservice on which the channel-scanning has failed.
 8. The verticalhandover method of claim 1, wherein the installing of the newapplication service comprises: generating and installing a controllerand resources required to execute the new application service; and if itis determined that the installation of the new application service hasbeen completed, executing the new application service.
 9. The verticalhandover method of claim 1, after the performing of the handover,further comprising: transmitting a service stop request to theapplication service which is currently being executed; and stoppinginstallation of the application service according to the service stoprequest.
 10. An apparatus for vertical handover which is included in aSoftware Defined Radio (SDR) terminal capable of selectively executingat least one of a plurality of application services, comprising: atleast one service execution unit which is software-reconfigurable andcapable of executing various application services; and a handoverexecution unit to perform a handover between the application servicesthat are executable by the SDR terminal; and a Software CommunicationArchitecture (SCA) core framework, when receiving a handover requestfrom the service execution unit which executes an application service,to generate a service execution unit for executing an applicationservice that is a handover target, and to control execution of ahandover of the SDR terminal in connection with the service executionunit and the handover execution unit.
 11. The apparatus of claim 10,wherein the SCA core framework comprises preferentially selecting anapplication service which has not recently been installed in the SDRterminal, based on installation history information about applicationservices executable in the SDR terminal.
 12. The apparatus of claim 11,wherein the SCA core framework comprises selecting the new applicationservice based on a Software Component Descriptor (SCD) and a SoftwareAssembly Descriptor (SAD) of a domain profile.
 13. The apparatus ofclaim 10, wherein the SCA core framework controls the entire operationof the SDR terminal.
 14. The apparatus of claim 10, wherein the handoverexecution unit comprises: a Layer3 (L3) resource to control a handoveroperation; a Media Independent Handler (MIH) resource to performhandover primitive processing between the application services that areexecutable by the service execution unit; and a handover assemblycontroller to process control commands between the L2 resource, the MIHresource, and the SCA core framework.
 15. The apparatus of claim 14,wherein the handover assembly controller, when receiving a handoverrequest from the service execution unit which executes the applicationservice, requests the SCA core framework to generate the serviceexecution unit for executing the application service which is thehandover target and requests the MIH resource to performchannel-scanning on the application service after the generation of theservice execution unit.
 16. The apparatus of claim 14, wherein the L3resource determines the result of the channel-scanning on theapplication service, and if the L3 resource determines that thechannel-scanning on the application service fails, the handover assemblycontroller requests the SCA core framework to generate a serviceexecution unit for executing another application service.
 17. Theapparatus of claim 14, wherein the handover assembly controller, whenreceiving a signal indicating radio signal disconnection from theservice execution unit which executes the application service, transmitsa service stop request for stopping execution of the application serviceto the SCA core framework and transmits the service stop request to theMIH resource when receiving a response to the service stop request. 18.The apparatus of claim 10, wherein the service execution unit comprises:a Medium Access Control (MAC) resource which controls a MAC layer; aPhysical Layer (PHY) resource which controls a physical layer; and aservice assembly controller to process control commands between the MACresource, the PHY resource and the SCA core framework.